US4121837A

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Info

Publication number: US4121837A
Application number: US05/804,818
Authority: US
Inventors: Noboru Tominari; Hiroshi Takahashi
Original assignee: Onlife Research Inc
Current assignee: TOMINARI ENGINEERING Ltd NO 8-6 3-CHOME GINZA CHUO-KU TOKYO; Onlife Research Inc
Priority date: 1976-06-11
Filing date: 1977-06-08
Publication date: 1978-10-24
Anticipated expiration: 1997-06-08

Abstract

A record player comprises a tone arm provided at the distal end thereof with a pickup cartridge, and a vibration damping device for damping a resonance of the tone arm. The damping device comprises a damping member made of an electrically conductive material and provided at the tone arm in a manner to vibrate unitarily therewith, and a damping unit inclusive of permanent magnet means for forming a magnetic field with respect to the damping member. Eddy currents are generated in the damping member when the damping member vibrates in the magnetic field, whereby damping of the vibration of the damping member and the tone arm is accomplished. The damping device may further comprise an elastic member supported at one end thereof at the tone arm and having another free end and a weight secured to the free end of the elastic member.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to record players having devices for absorbing or damping the vibrations of their tone arms, and more particularly to a record player in which is provided a vibration absorbing or damping device for effectively damping unwanted resonance due to the compliance of a cantilever of a pickup cartridge and to the equivalent inertial mass of the tone arm.

In a record player, in general, a resonance phenomenon referred as a so-called arm resonance occurs as a result of the compliance of the cantilever of the pickup cartridge and the equivalent inertial mass of the tone arm. This arm resonance produces a peak of the order of 10 to 20 dB in the vicinity of approximately 5 to 10 Hz in a frequency characteristic, depending on the values of the above mentioned compliance and the equivalent inertial mass. For this reason, this arm resonance gives rise to a deterioration of the reproducing characteristics at low frequencies.

The reproducing performance of a tone arm may be broadly divided into a low-frequency reproducing performance and a tracing performance. In order to improve the low-frequency reproducing performance, it is necessary to decrease as much as possible the unwanted resonance peak due to the above mentioned arm resonance thereby to suppress the occurence of effects of cross-modulation distortion and the like. One expedient for preventing the occurrence of this arm resonance would appear to be to increase the resistance of the rotational pivot point of the tone arm thereby to damp the arm resonance.

However, the trend in recent years has been toward a reduction to a minimum of the resistance of this rotational pivot point of the tone arm in order to improve the above mentioned tracing performance. Consequently, if the pivot resistance of the tone arm were to be increased in order to damp the arm resonance, the tracing performance would be caused to deteriorate. Accordingly, it has not been possible to satisfy the improvements of both the low-frequency reproducing performance and the tracing performance by suitable selection of the value of the pivot resistance of the tone arm.

Therefore, there has been a need for a record player in which the pivot resistance of the tone arm is made low thereby to improve the tracing performance, and the arm resonance is reduced by some means thereby to improve the lowfrequency reproducing performance.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a novel and useful record player having a device for absorbing or damping vibrations of the tone arm which satisfies the above stated needs.

Another and specific object of the invention is to provide a record player having a vibration absorbing device for attenuating or damping the resonant vibration of the tone arm thereby to reduce the arm resonance without increasing the pivot resistance of the tone arm.

Still another object of the invention is to provide a record player having a vibration absorbing devide for damping resonant vibration of the tone arm by utilizing eddy current loss due to electromagnetic induction.

A further object of the invention is to provide a record player having a vibration absorbing device including a dynamic damper for damping resonant vibration of the tone arm by coupled vibration.

Other objects and further features of the invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a plan view of one embodiment of a record player constituting a preferred embodiemtn of the invention;

FIG. 2 is a side elevation of the record player illustrated in FIG. 1;

FIG. 3 is a perspective view, with parts cut away, showing the essential parts of the same record player;

FIG. 4 is a bottom perspective view of one art of the tone arm of the same record player;

FIG. 5 is a plan view showing an essential part of the record player shown in FIG. 1 with the tone arm in rotated state;

FIG. 6A and 6B are diagrammatic model views respectively representing vibration systems wherein dynamic dampers are considered;

FIG. 7 is a diagrammatic model view of a vibration system wherein an electromagnetic damper is considered;

FIGS. 8A, 8B, 8C, and 8D are graphs respectively indicating frequency characteristics of response in the case where a damper is not used, the case where only a dynamic damper is used, the case where a dynamic damper and an electromagnetic damper are used, and the case where only an electromagnetic damper is used;

FIG. 9 is a partial perspective view showing one embodiment of a vibration damping device provided in a sub-arm of a tone arm of the record player; and

FIG. 10 is a partial perspective view showing another embodiment of a vibration damping device provided in the sub-arm.

DETAILED DESCRIPTION

In therecord player 10 illustrated in FIGS. 1 through 3, thetone arm 11 comprises amain arm 12 and asub-arm 13. Themain arm 12 can swing freely in a horizontal plane about avertical shaft 14 supported by ablock 44, and can move in a vertical plane together with theblock 44 which is fixed to a horizontally extendingshaft 16 rotatably supported by ablock 15. Thesub-arm 13 is rotatably supported in a manner permitting it to swing freely in a vertical plane at a styluspressure adjusting device 17 mounted on the forward end part of themain arm 12. Acartridge shell 18 for loading a pickup cartridge is mounted on the forward end part of thesub-arm 13, and acounterbalance weight 19 is adjustably secured to the rear part of thesub-arm 13.

Acounterbalance weight 20 is mounted on the rear part of themain arm 12. Asupport post 21 is fixed to the lower surface of the rear end of themain arm 12 and fixedly supports one end of anarcuate damping plate 22 made of an electrically conductive material and lying in a horizontal plane, the center of the arc of its arcuate shape being the above mentionedvertical shaft 14. Adamping unit 23 is fixedly mounted on the outer end of theshaft 16. Thisdamping unit 23 comprises asupport member 24 fixed to the outer end of theshaft 16 and a pair of

permanent magnets

26a and 26b confronted with agap 25 therebetween and fixedly supported by thesupport member 24.

When thetone arm 11 is swung in a horizontal plane about theshaft 14 toward the record playing position, thedamping plate 22 is inserted from its outer free end into thegap 25 of thedamping unit 23 in a state wherein it does not contact the

permanent magnets

26a and 26b, as indicated in FIG. 5. If, during the playing of a record when thedamping plate 22 is inserted in thegap 25 of thedamping unit 23, thetone arm 11 is swung upward in order to stop the playing of the record, the rotation of thetone arm 11 will not be obstructed by thedamping plate 22 and thedamping unit 23 since thedamping unit 23 rotates together with theblock 44 and thetone arm 11, being connected thereto by way of theshaft 16.

The above mentionedblock 15 is vertically movable on and relative to asupport post 28 embeddedly fixed at its lower end to abase structure 27. By turning aknob 29 provided at the side of thisblock 15, theblock 15 is moved up and down unitarily with thetone arm 11, theblock 44, theshaft 16 and thedamping unit 23 thereby to set the height position thereof.

The structural part of themain arm 12 is of substantially channel form, and supports a supportingmember 30 fixed to its bottom surface in the vicinity of theshaft 14 as best shown in the bottom perspective view of FIG. 4. Aleaf spring 31 disposed longitudinally within themain arm 12 is fixed at its rear end to the supportingmember 30 and supports at its front free end aweight 32, which is adjustably set in longitudinal position relative to theleaf spring 31 by ascrew 33. Theleaf spring 31 is disposed such that the plane thereof is vertical and is horizontally swingable.

The aforementioned styluspressure adjusting device 17 has acylindrical casing 35 with areference line 34 marked thereon and a styluspressure adjusting knob 36 rotatably supported at an end part of thecasing 35 and having inscribed on its outer periphery acalibration scale 37 indicating the stylus pressure in conjunction with thereference line 34. Theknob 36 and adisc 38 are pressed against abearing retainer 39 by a disk shape spring (not shown). The inner end of aspiral spring 40 is fixedly anchored to atransverse shaft 41, while the outer end of thespiral spring 40 is fixed to apin 42 fixed to thedisc 38 and theknob 36. Here, the force of thespiral spring 40 is less than the pressing force of theknob 36 and thedisc 38 against thebearing retainer 39. Thetransverse shaft 41 is fixed to aholder 43 of thesub-arm 13.

When theknob 36 is turned, thepin 42 also undergoes rotational displacement unitarily therewith, and the force of thespiral spring 40 is adjusted. Thus, the torque exerted on theshaft 41 by thespiral spring 40 is adjusted, and, accordingly, the pressing force of the stylus of the pickup cartridge is adjusted by way of thesub-arm 13. The stylus pressing force at this time is indicated by thereference line 34 on thestylus force scale 37 on theknob 36.

Anarm rest 45 is supported by asupport rod 46 secured to theblock 44. Thearm rest 45 has a cut outrecess 45a which has a vertical inner wall surface and into which themain arm 12 fits. Apermanent magnet 47 for attracting themain arm 12 and holding the same in its rest position is embedded in the inner wall surface of the cut out recess.

The vibration system of thetone arm 11 inclusive of the dynamic damper comprising theleaf spring 31 and theweight 32 will now be considered. The general composition of this vibration system is indicated in FIG. 6A. For the following analysis: the spring constant of theleaf spring 31 constituting an elastic structure of the dynamic damper will be designated by k; the mass of theweight 32 by md; the compliance of the cartridge by c; and the equivalent mass of thetone arm 11 by m. The arm resonance frequency of thetone arm 11 is represent as follows. ##EQU1## Furthermore, the resonance frequency of the dynamic damper, fd, is expressed as follows. ##EQU2##

Then, by making the above frequencies f and fd equal to each other, the peak of the arm resonance is changed to a dip in a frequency characteristic by the coupled vibration of the arm system and the dynamic damper system.

A frequency characteristic accompanied by the arm resonance of thetone arm 11 in the case where the above described dynamic damper and the electromagnetic damper comprising the dampingunit 23 and the dampingplate 22 are not used is as indicated in FIG. 8A. As is apparent from this graph, the characteristic is substantially flat at frequencies above approximately 15 Hz, but there is a large peak at approximately 5 Hz because of arm resonance. It can be observed, furthermore, that a peak is produced also at approximately 10 Hz.

Accordingly, by providing a dynamic damper comprising theleaf spring 31 and theweight 32, the peak at 5 Hz is changed into a dip in the frequency characteristic by the above mentioned coupled vibration, and the characteristic of the entire system becomes as indicated in FIG. 8B.

A method of designing a dynamic damper so that it will produce a coupled vibration such as to change the peak into a dip in the frequency characteristic as mentioned above will now be described. In the vibration system illustrated in FIG. 6B, it will be assumed that, as one specific example: the cartridge compliance c is 15 × 10^-6 cm./dyne; the effective length l₁ of the tone arm is 24 cm.; the distance l₂ from the pivot support point to the center of the balance weight is 7 cm.; the distance l₃ from the pivot support point to the center of the sub-arm is 16 cm.; the mass m_w of the balance weight is 200 grams (gr.); and the total mass m_s of the front part of the tone arm is 100 gr. Then, the moment of inertia J is determined as follows.

J = J.sub.1 + J.sub.2 = m.sub.s l.sub.3.sup.2 + m.sub.w l.sub.2.sup.2 = 3.54 × 10.sup.4 (dyne.cm.sec.sup.2.)

The resonance point frequency f is then as follows. ##EQU3## Here, the rigidity of theleaf spring 31 is as follows. ##EQU4## Here, if it is assumed that: the constant E is 1.1 × 10⁴ Kgr./mm.² in the case where phosphor bronze is used for theleaf spring 31; the leaf spring width b is 4mm.; the leaf spring thickness t is 0.2 mm., and the poisson ratio is 0.3, then, ##EQU5## If the mass md of theweight 32 used is taken as approximately 7 gr., from the equation ##EQU6## for the resonance frequency fd, the value of K is as follows. ##EQU7## Accordingly, in order to obtain a resonance point of the dynamic damper of 5 Hz, the length l of theleaf spring 31 must be as follows. ##EQU8## Therefore, in the case of the above example of numerical values, by securing theweight 32 at a position approximately 51.7 mm. from thesupport member 30 of theleaf spring 31, a characteristic as indicated in FIG. 8B is obtained as a result of the coupled vibration.

On the other hand, when the tone arm has been swung to its record playing position, the dampingplate 22 is inserted in thegap 25 of the dampingunit 23. Accordingly, when the tone arm vibrates in the horizontal direction as a result of the arm resonance, the dampingplate 22 also vibrates in the horizontal direction in thegap 25 of the dampingunit 23.

In general, within an electrical conductor moving in a uniform magnetic field, electric eddy currents are caused to flow by electromagnetic induction. This eddy current flow within a plane perpendicular to the magnetic flux generates Joule heat, giving rise to a heat loss. This eddy current loss hinders the movement of the conductor within the magnetic field. Here, the damping coefficient Cd is expressed by the following equation in relation to the volume V of the air gap forming the magnetic field, the resistivity ρ of the conductor, and the magnetic flux density B. ##EQU9## A general vibration model is illustrated in FIG. 7.

A magnetic field is established in thegap 25 by the

permanent magnets

26a and 26b of the dampingunit 23. For this reason, when the dampingplate 22 is caused to vibrate within thisgap 25 by the arm resonance as described hereinabove. eddy currents are cuased to flow in the dampingplate 22 made of conductor by electromagnetic induction, and the vibration of this dampingplate 22 is damped as a result of the loss thus produced.

Accordingly, when this electromagnetic damper is used in conjunction with the aforedescribed dynamic damper, the small crests and valleys in the characteristic indicated in FIG. 8B are smoothed flat, and a characteristic which, as a whole, is as indicated in FIG. 8C, is obtained.

This electromagnetic damper need not be used in conjunction with a dynamic damper. When only a damping means comprising the above described dampingunit 23 and dampingplate 22 is used, a characteristic as indicated in FIG. 8D is obtained. As is apparent from a comparison of FIG. 8A and 8D, the peak due to the arm resonance is reduced.

Since, in the instant embodiment of the invention, the diameter of the

permanent magnets

26a and 26b is 19 mm., and the gap of theair gap 25 is 2 mm., for example, ##EQU10## Furthermore, in the case where B is 5,000 gauses, and copper is used for the dampingplate 22,

ρ = 1.7 × 10.sup.-8

Therefore, ##EQU11##

The above described embodiment of the invention has a structural arrangement wherein the vibration damping device comprising damping means is provided on themain arm 12, and vibration of thetone arm 11 in the horizontal plane is damped, but an alternative arrangement wherein the vibration damping device is provided on the sub-arm 13, and vibration in a vertical plane is damped may be used. Embodiments of this alternative arrangement of the invention will now be described with reference to FIGS. 9 and 10.

In FIG. 9, those parts which are the same as corresponding parts in FIG. 3 are designated by like reference numerals. Detailed description of such parts will be omitted. On the outer side of theknob 36, a dampingdisc 50 made of an electrically conductive material is fixed to the outwardly extending end of theshaft 41, and, furthermore, acoil spring 51 is fixed coaxially with this dampingdisc 50. A disc-shapedweight 52 is fixed to an end part of thecoil spring 51. Thecasing 35 has aprojection 53 supporting, by way of abeam 54, a holdingmember 55. The holdingmember 55 holds a pair ofpermanent magnets 56 forming therebetween a gap into which the dampingdisc 50 is inserted.

When the sub-arm 13 vibrates up and down in a vertical plane, the dampingdisc 50 also undergoes rotational vibration together with theshaft 41. Here, thecoil spring 51 and theweight 52 constitute a dynamic damper. Furthermore, thepermanent magnets 56 and the dampingdisc 50 constitute an electromagnetic damper. Therefore, as is easily understandable from the operation of the above described embodiment of the invention, the vertical vibration of the sub-arm 13 is effectively damped by these dampers.

In another embodiment illustrated in FIG. 10, those parts which are the same as corresponding parts in FIGS. 3 and 9 are designated by like reference numerals. Detailed description of these parts will not be repeated. On the outer side of theknob 36, a dampingplate 60 of fan or sector shape made of an electrically conductive material is fixed to the outwardly extending end part of theshaft 41. The dampingplate 60 is inserted into a gap between the pair ofpermanent magnets 56. Aweight 62 is suspended by way of aleaf spring 61 from the lower part of the dampingplate 60 on the side of theshaft 41 opposite from the sector-shaped part of the dampingplate 60.

When the sub-arm 13 vibrates up and down in a vertical plane, the dampingplate 60 also undergoes swinging vibration together with theshaft 41. Here, theleaf spring 61 and theweight 62 constitute a dynamic damper, while thepermanent magnets 56 and the dampingplate 60 constitute an electromagnetic damper. These dampers function to effectively damp the vibration of the sub-arm 13.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope and spirit of the invention.

Claims

What is claimed is:

1. A record player comprising:

a tone arm having a main arm and a sub-arm, said sub-arm being pivotably mounted with a shaft on a forward end of the main arm to rotate in swinging movement in a vertical plane and having a pickup cartridge mounted thereon;

pivoting means for pivoting the main arm with a pivot shaft to rotate in swinging movement in a horizontal plane;

a damping plate made of an electrically conductive material having a substantially arcuate shape and secured to said main arm projecting in a lateral direction thereof;

a damping unit having a pair of permanent magnets with a gap therebetween for insertion therein of said damping plate to form a magnetic field within said gap, said damping plate being displacable in the gap between the permanent magnets with swinging motion of the main arm; support means for supporting the damping unit in a position whereby the damping plate being insertable into the gap between the permanent magnets;

a leaf spring supported at a first end thereof at said main arm whereby a second free end being adapted to vibrate in a horizontal plane and extends in a longitudinal direction of the main arm; and

a weight being secured to said second end of said leaf spring.

2. A record player as claimed in claim 1, further comprising: a first block for holding said pivoting means being rotatable integrally with the main arm in a vertical plane; said support means being defined by a horizontal shaft provided integrally with said first block; and a second block for bearing upon said supporting means so that the main arm, first block, and damping unit rotate in the vertical plane.

3. A record player as claimed in claim 2 further comprising: a base structure; and means for adjustably supporting the second block with respect to the base structure.

4. A record player comprising:

a tone arm having a main arm and a sub-arm; said sub-arm being pivotably mounted with a shaft on a forward end of the main arm to rotate in swinging movement in a vertical plane and having a pickup cartridge mounted thereon;

a damping plate formed of an electrically conductive material secured to said sub-arm to project in a vertical direction thereof;

a damping unit formed of a pair of permanent magnets having a gap therebetween for insertion therein of said damping plate to form a magnetic field within said gap, said damping plate being displacable in the gap between the permanent magnets with swinging motion of the sub-arm, and said damping unit being supported by the main arm.

5. A record player as claimed in claim 4, comprising: an elastic member being supported substantially at one end thereof at said sub-arm and having another free end and a weight secured thereto.